Growing up on his parents' farm, Piotr Rasputin saw his older brother Mikhail become a Cosmonaut. Mikhail was later discovered to be a latent mutant with energy warping powers, and to keep him secret the government faked his death. In later years, Piotr learned that he too was a mutant, and could transform his flesh into steel, but he was content to use his powers to help his fellow farmers. When a transformed Piotr rescued his sister Illyana from a runaway tractor, he was approached by Professor Charles Xavier, who was recruiting mutants for a new team of X-Men to help save his original students from the sentient island Krakoa. Dubbed Colossus by Xavier, Piotr reluctantly joined this new team, which freed the original X-Men and helped defeat Krakoa. After the battle, Piotr remained with the X-Men in America, though he found it difficult to adjust to living in a different culture.

Piotr had many adventures with the X-Men. Later, the X-Men recruited young mutant Kitty Pryde. Despite their initial shyness, a romance blossomed between her and Colossus. Later, the villain Arcade's assistant Miss Locke kidnapped the X-Men's loved ones, including Illyana, to coerce the team into rescuing Arcade from the despotic Doctor Doom. The X-Men rescued them, and Illyana remained with her brother at Xavier's mansion. Eventually, Illyana was trapped in the demon-filled realm Limbo by its then-master, Belasco. She remained his captive for many years, though only moments had elapsed on Earth, and returned as the adolescent sorceress Magik.

Colossus and Kitty grew closer, finally admitting their feelings for one another. Colossus was among the X-Men forced by the godlike Beyonder to fight on his Battleworld. There, he fell in love with the healer Zsaji. After Colossus was killed by a cosmic-powered Doom, Zsaji gave her life to resurrect him. A heartbroken Colossus returned to Earth, ending his relationship with Kitty, though they remained friends.

After a failed demonic invasion of New York, Illyana regressed in age. Colossus believed she would be safer away from the X-Men and sent her home to Russia. Later, the Russian government invaded the Rasputin home, killing Colossus' parents and capturing Illyana, whom they sought to genetically accelerate to combat the threat of the mutant Soul Skinner. She was soon rescued by Colossus and came to live with him in America. Eventually, Illyana fell victim to the mutant-killing Legacy Virus, and a disillusioned Colossus abandoned Xavier's dream, joining Magneto's disciples, the Acolytes. Peter would care for the mindwiped Magneto after Professor X avenged Wolverine's injuries at the master of magnetism's hands. Later on, Piotr searched for Kitty, then a member of the British super-team Excalibur. When he found Kitty kissing her then-boyfriend Pete Wisdom, Colossus nearly beat Wisdom to death in a jealous rage. Excalibur took responsibility for Colossus, and he came to accept his role with the team, serving as a valued member until they disbanded, after which Colossus rejoined the X-Men. When Xavier temporarily disbanded the X-Men in an effort to flush out an alien impostor, Colossus and his teammate Marrow set off on vacation, but were instead teleported to the Hill. There, Colossus freed his brother Mikhail from the corrupting influence of a sentient energy being and took him back to Earth. Soon after, during a clash between the X-Men and the forces of Apocalypse, Mikhail used his powers to teleport Apocalypse's Horsemen to parts unknown.

Following the death of renowned geneticist Moira MacTaggert, the X-Men's resident scientist the Beast used her work to create a cure for the Legacy Virus; however, it could not be activated without emulating the manner in which the plague had first been discharged: through the death of an infected mutant. Having stood by, powerless, as his sister succumbed to the virus, Colossus injected himself with the formula. The serum caused his powers to flare, spreading the cure into Earth's atmosphere, claiming his life in the process. Colossus' body was supposedly cremated, and Kitty scattered the ashes over his Russian farmland home; however, his body had secretly been stolen by Ord, an alien who had learned that an Earthly mutant would be responsible for destroying his world. Ord had come to Earth to declare war, but the spy agency S.W.O.R.D., a sub-division of S.H.I.E.L.D. handling extraterrestrial matters, was able to settle diplomatically with him. Ord had Colossus restored to life and imprisoned him for years while experimenting on him. Ultimately, Ord discovered the Legacy Virus cure still in Colossus' system and presented his findings to Benetech geneticist Doctor Kavita Rao, who modified it to create a "cure" for the "mutant condition." Learning of the cure, the X-Men went to Benetech to investigate. There, Kitty found Colossus alive and, after overcoming her initial shock, took him to aid the X-Men against Ord. Defeated, Ord was taken into custody, and Colossus returned home with the X-Men to adjust to his new lease on life.

After breaking out of custody, Ord once again attacked Colossus and the X-Men. In the midst of battle, the X-Men were pulled from Earth by S.W.O.R.D. in order to deal with the increasingly hostile situation with Breakworld. Aboard the S.W.O.R.D. ship, it was revealed that Colossus is the mutant destined to destroy Breakworld. Later Breakworld fires a giant bullet at earth to destroy the planet. Kitty Pryde bonds with the bullet and makes it intangible so that it will pass harmlessly through earth. She is unable to free herself from the bullet, however, and is lost in space. In grief due to losing Kitty, Piotr leaves the X-Men.

Bloodlines

Piotr learns of Kitty’s return to the X-Men due to the efforts of Magneto. He returns to Xavier’s school to help her adjust to her return to earth.

During Fear Itself, Piotr fights Juggernaut during his escape from the Raft. He becomes the Avatar of Cytorrak during this time.

Powers and Abilities

Organic Steel Transformation: Colossus is a mutant with the superhuman ability to convert the tissue of his entire body into an organic steel-like substance. This substance resembling steel is of unknown composition but appears to be analogous to osmium and to carbon steel. He is able to transform into this armor-like state at will (the process is virtually instantaneous) and remain in that form for an as yet undetermined amount of time. Once in his armored form he remains so until he consciously wills himself back to normal. If he is rendered unconscious, however, he spontaneously reverts to his normal form. While in the armored state, Colossus possesses the same degree of mobility that he does in his normal form.

Superhuman Strength: After transforming into his armored state, Colossus possesses vast superhuman strength. As a teenager, he was sufficiently strong enough to lift about 70 tons. However, as a fully mature adult, his strength has increased to the point that he is able to lift up to 100 tons.

Superhuman Stamina: Also, while in armored form, Colossus' musculature produces considerably less fatigue toxins than the musculature of a normal human. At his peak, he can physically exert himself at peak capacity for several days before the build-up of fatigue toxins in his blood begins to impair him.

Superhuman Durability: In his armored form Colossus is invulnerable to most forms of bodily harm. His armor is capable of withstanding ballistic penetration, including that of a 110 millimeter Howitzer shell. He can survive extremes of temperature from 70 degrees above absolute zero to approximately 9000 degrees Fahrenheit. He can survive a collision with a loaded, one-ton flatbed truck at 100 miles per hour or an explosion of 450 pounds of TNT. He can also survive falls from great heights while in his armored body.

Expert Melee Combatant: Colossus is an excellent hand-to-hand combatant, having received training from Wolverine and Cyclops. He has had training in acrobatics and sword fighting from Nightcrawler. In his human form, he is exceptionally strong and fit, though not superhumanly so.